The thesis examines the nature of third-party intervention in industrial disputes, from the perspective of bargaining and negotiation. It challenges the common view of the third-party as encouraging a conciliatory approach to the dispute. Experimental simulation provides evidence that a silent third-party affects the nature of agreements reached by negotiators, in this case favouring management. The third-party was regarded as an evaluative presence, encouraging greater intransigence and emphasising the inter-party dispute, at the cost of a more cooperative, personally-oriented approach. An observational field study of third-party intervention in public and private sector disputes examines the functions and process of industrial arbitration, through the British Advisory Conciliation and Arbitration Service, for relatively inexperienced and experienced participants. Arbitration is traditionally regarded as a semi-judicial, evaluative process, which is distinct from negotiation. It is argued that this public image is necessary, in order to maintain the credibility of arbitration as a method of dispute resolution, but that the actual process is best understood in terms of the social context of collective bargaining. The process of arbitration is compared and contrasted with the processes of problem-solving and negotiation and two different models of negotiation (‘concession convergence’ and ‘formula-detail’) are used to explain the different roles adopted by the arbitrator or board in simpler and more complex disputes respectively. A descriptive account of a group of ad hoc arbitrations highlights the effects on inexperienced participants of the evaluative image of arbitration and reaffirms the distinction, identified in the public sector disputes, between simpler and more complex cases, requiring different styles of chairmanship.